An embodiment of the invention is directed to an electrochemical method for removing sulfur from a hydrocarbon stream, preferably a naphtha feedstream while preserving octane number.
Due to environmental regulations the amount of sulfur present in gasoline streams must be closely controlled. Gasoline is typically made up of a mixture of (1) naphthas from fluid catalytic cracking processes, (2) reformate from catalytic reforming processes, (3) alkylate from acid-catalyzed alkylation processes and (4) various additives. Almost all of the sulfur in gasoline is contributed by the naphtha component. The regulations will require the amount of sulfur in gasoline to be reduced to about 150 ppm by the year 2000, with further reduction to about 30 ppm by the year 2004. Thus, there is a critical need for technologies that are capable of lowering the amount of sulfur present in naphtha streams.
Present technology for lowering the amount of sulfur in naphtha streams, which is based on catalytic hydrotreating, results in an octane loss due to saturation of olefins present in the naphthas. Thus, following the sulfur removal, octane must be replaced. In the Mobil Oct-Gain and Intevep ISAL processes, for instance, the desulfurized product is isomerized, resulting in an increase in octane but at a substantial yield loss.
An embodiment of the invention is directed to an electrochemical process for removing polymerizable sulfur compounds from a hydrocarbon feed comprising the steps of:
(a) combining a solvent and electrolyte with a feed comprising hydrocarbon and polymerizable sulfur compounds to form a first mixture;
(b) passing said first mixture into an electrochemical reactor to electro-chemically oxidize said polymerizable sulfur compounds in said mixture under conditions capable of producing sulfur oligomers from said polymerizable sulfur compounds;
(c) separating said oxidized first mixture and recovering a desulfurized hydrocarbon feed, and a second mixture comprising sulfur oligomers, solvent and electrolyte.
An embodiment of the invention may further comprise step (d) recycling said second mixture to said step (a).
An embodiment of the invention may optionally comprise (d) separating said sulfur oligomers from said second mixture to recover a stream comprising solvent and electrolyte; and
(e) recycling said stream comprising solvent and electrolyte to said step (a).